Download The Digestive System

The Digestive
System
“You are what you eat!”
Try to label the diagram (PENCIL!!)
What is Digestion?
• Digestion: the breakdown of large
macromolecules (proteins, fats,
carbohydrates) into smaller molecules
so that they can be absorbed by the
circulatory system and used by cells
 Proteins
 amino acids
 Fats
 triglycerides
Carbohydrates  sugars
(glucose, sucrose, lactose etc.)
The Digestive System…
Consists of…
• Alimentary canal/Gastrointestinal
tract: 6-9 meters long! Extends from
mouth all the way to the anus. Includes
the mouth, esophagus, stomach, small
intestine, large intestine, rectum and
anus
 Pathway food takes
The Digestive System…
Consists of…
• Associated Organs: connected to the
gastrointestinal system via a series of
ducts. Include the salivary glands,
liver, gall bladder, pancreas
Four Steps of Digestion
1) Ingestion: the taking IN of nutrients
(eating)
2) Digestion: the mechanical and chemical
breakdown of food into molecules
3) Absorption: the passing of the broken
down molecules into the bloodstream
(mostly done in small intestine)
4) Elimination/Egestion: the removal of
solid waste (undigested food) from the
body
2 Processes of Digestion
1) Mechanical/Physical Digestion:
Involves chewing, mashing, chopping,
breaking food into smaller pieces and
physical movement of food
2) Chemical Digestion: Involves enzymes
to break food down into macromolecules
and nutrients needed at the cellular level
(via hydrolysis)
The Pathway of Food
1) Mouth (ingestion, digestion  mech+chem)
 Mechanical digestion begins:
o
Chewing breaks food down into smaller particles so
that chemical digestion can occur faster
 Chemical digestion begins:
o
3 pairs of salivary glands



Parotid glands
Sublingual glands
Submandibular (Submaxillary) glands
The Pathway of Food
1) Mouth (ingestion, digestion  mech+chem)
 Chemical digestion begins:
o
3 pairs of salivary glands



o
Secrete saliva which contains:



o
Parotid glands
Sublingual glands
Submandibular (Submaxillary) glands
Mucus keeps food moist, gets rolled into a bolus by the
tongue
Salivary amylase begins to breakdown starch
Maltase converts maltose  glucose
Secretion is stimulated by the presence of FOOD
 Tongue is a muscle that pushes food to back of
mouth where it is swallowed)
The Pathway of Food
2) Esophagus
 Swallowing reflex takes over to move the bolus
down the esophagus
o
The esophagus is lined by a film of slippery mucous
to aid the bolus in moving down
 Bolus is moved to
the stomach by
“peristalsis”
o
Rhythmic
muscle
contractions
The Pathway of Food
3) Stomach (digestion  mech+chem)
 Cardiac sphincter controls movement of bolus
into the stomach and prevents stomach acid
from re-entering the esophagus
 Salivary amylase swallowed from the mouth
continues to digest starch until the pH gets too
low! (amylase does NOT function at low pH
levels!)
The Pathway of Food
3) Stomach (digestion  mech+chem)
 Glands in the stomach lining secrete gastric
juice containing:
i.
Hydrochloric acid (HCl)



Keeps stomach contents at pH 1-3, aids in digestion
Low pH also kills most pathogens
Stomach lining is protected by a regenerating coating
of mucus
 Stomach ulcers  Heliobacter pylori
The Pathway of Food
3) Stomach (digestion  mech+chem)
 Glands in the stomach lining secrete gastric
juice containing:
ii. Pepsin (HCl + pepsinogen)




Digests proteins (proteins  polypeptides)
~2L of acid/gastric secretions produced per day
Senses can increase the production/secretion of these
gastric juices
Carbohydrates (CHO) and
fats (LIP) are NOT broken down
in the stomach; too acidic,
enzymes are inhibited!
 Partially digested liquid food in
acid is now called “chyme”
The Pathway of Food
4) Small Intestine (digestion  chem,
absorption)
 Approx. 7 meters long
 Pyloric sphincter regulates movement of
chyme into the small intestine in small spurts
 Divided into 3 sections:
i.
Duodenum


Digestion of proteins and carbohydrates finishes
Digestion of fats begins
ii. Jejunum
iii. Ileum
The Pathway of Food
4) Small Intestine (digestion  chem,
absorption)
 Associated organs:
i.
LIVER:

Produces bile salts/bile to emulsify (dissolve) fats
ii. GALL BLADDER:


Stores bile until needed
Common bile duct connects the liver and gall bladder to
the duodenum to release bile into the small intestine
**if the common bile duct becomes blocked, bile salts can
accumulate in the skin or blood and produces a yellow
colour in a condition called jaundice**
The Pathway of Food
4) Small Intestine (digestion  chem,
absorption)
 Associated organs:
iii. PANCREAS: Produces pancreatic juice which is released
into the duodenum via the pancreatic duct
 Sodium bicarbonate neutralizes chyme, leaving small
intestine basic (pH ~ 9)
 28 digestive enzymes, some of which are:
a) Trypsin (polypeptides  peptides)
b) Peptidase (peptides  animo acids)
c) Lipase (fats  fatty acids and glycerol)
d) Maltase/Sucrase/Lactase (Disaccharides 
Monosaccharides)
**Some people do NOT produce lactase = Lactose Intolerant)
• Pancreas also produces insulin, Type 1 diabetes (immune
system destroys insulin-producing cells of pancreas)
THEREFORE: Insulin isn’t produced and glucose builds up in
blood
The Pathway of Food
4) Small Intestine (digestion  chem,
absorption)
 Inner walls of intestine are covered small
projections called villi and these are covered
with even tinier projections called microvilli
(“brush border”)
  surface area
The Pathway of Food
4) Small Intestine (digestion  chem,
absorption)
 Each villus has a blood supply of capillaries
where the nutrients resulting from digestion
are absorbed into the blood by diffusing
through the cells of the intestinal lining
The Pathway of Food
5) Large Intestine (absorption; egestion)
 Ileocaecal valve prevents waste products from
re-entering the small intestine
 Water and minerals are absorbed from
undigested food
 Bacteria helps to further breakdown the
undigested food
i.
ii.
iii.
iv.
v.
Cecum
Ascending Colon
Transverse Colon
Descending Colon
Sigmoid Colon
The Pathway of Food
6) Rectum and Anus (egestion)
 Rectum stores waste which is then expelled
Try to label the rest of the Digestive System
Diagram…before we take it up!